The present invention relates to a power transmission system for a four-wheel drive motor vehicle, and more particularly to a system having a fluid operated multiple-disk friction clutch. This type of clutch is employed in a transfer device for distributing the output torque of a transmission to auxiliary drive wheels.
In such a vehicle, the power transmission system can be converted from a two-wheel drive system to a four-wheel drive system by engaging the clutch.
In the four-wheel drive vehicle, there are several layouts of the engine and power trains, such ar a front-mounted engine with front-wheel drive layout, a front-mounted engine with rear-wheel drive layout, and a rear-mounted engine with rear-wheel drive layout.
Since distribution between the front axle load and the rear axle load is varied in accordance with the engine an power train layout of the four-wheel drive motor vehicle, it is desirable to design the torque transmission system in accordance with the distribution of axle load.
In the layout where the engine and the transmission are mounted on a front portion of the vehicle, the distribution cf the front axle load is larger than the rear axle load. However, the rear axle load becomes large in some layouts.
It is desired that the engine power is directly transmitted to the front wheels or the rear wheels in accordance with the layout of the drive line and the distribution of the axle load of the four-wheel drive motor vehicle, thereby improving driveability, driving stability and fuel consumption.
Japanese Patent Application Laid-Open 62-143720 discloses a four-wheel drive motor vehicle having a front-mounted engine with rear-wheel drive layout where a transmission output shaft is connected to rear drive wheels and a fluid operated friction clutch is provided on the output shaft. The engine power from the clutch is transmitted to the front wheels of the vehicle through a pair of gears, a shaft provided outside the transmission and a front differential.
Japanese Patent Application Laid-Open 62-23823 discloses a four-wheel drive motor vehicle in which the engine power is derived from a fluid operated friction clutch provided on a transmission output shaft through sprocket wheels and chains.
Since, in the former prior art, the four-wheel drive motor vehicle having the front-mounted engine with rear-wheel drive layout is constructed on the basis of the two-wheel drive motor vehicle having the front-mounted engine with rear wheel drive layout, it is difficult to alter the system to a front-wheel drive four-wheel system.
In the latter four-wheel drive motor vehicle, if the front-mounted engine with rear-wheel drive layout is altered to the front-mounted engine with front-wheel drive layout, problems arise in structure around the transfer clutch, hydraulic circuit for the clutch, structure of bearings, and extension of the case in the axial direction. These problems obstruct the alteration of the layout.